Blue,
My truck is is also 6v. But,……. I have 12v rear break and turn signals lights to improve rear visibility to following drivers.
You can do the same to get that 12v horn to work on a 6v truck very cheaply and easy. Purchase a 6v to 12v step up transformer.
Tie the 6v leg after your horn relay and the 12v leg to your horn!
Jim


~ Jim Schmidt, Bucks County, PA
1953 Chevrolet 3804 1-ton
In the DITY Gallery